The combination of trimethoprim (TMP) and sulfamethoxazole (SMX) is used in the treatment of many common infections such as urinary, respiratory and gastrointestinal tract infections. The aim of this study was to determine TMP and SMX simultaneously in human plasma samples by high performance liquid chromatography (HPLC) using antipyrine as the internal standard. Separation of the compounds was achieved on a reverse-phase C8 column packed with 5 microm dimethyl octadecylsilyl bonded amorphous silica (4.6 mm x 250 mm) column using a mobile phase consisted of potassium hydrogen phosphate, acetonitrile, methanol and water adjusted to pH 6.2. The mobile phase was delivered at a flow rate of 1 mL min- and the effluent was monitored using Max plot technique at 25 derees C. Retention times were 5 min for TMP, 7 min for antipyrine and 9 min for SMX. Quantitation limits were 10 ng mL(-1) for TMP and 50 ng mL(-1) for SMX. Our findings indicated that the developed HPLC method was precise, accurate, specific and sensitive for simultaneous determination of TMP and SMX. Proposed HPLC method was successfully applied for the analysis of TMP and SMX in human plasma after oral administration of a co-trimoxazole tablet to human volunteers.

Hepatic disposition of trimethoprim (TMP) and sulfamethoxazole (SMX) and the liver distributional volumes were investigated in the in situ perfused rat liver preparation. Perfusion experiments were conducted using Krebs-bicarbonate buffer delivered via the portal vein (15 ml/min) in a single-pass mode. Erythrocytes (intravascular marker) and Evans blue (extracellular marker) were used for the estimation of liver distributional volumes, and desiccation and freeze-drying methods were used for the estimation of liver water content. TMP and SMX were administered together as a bolus in the presence (1%) and absence of protein. Although SMX profiles displayed a characteristic sharp peak followed by a slower eluting tail in all cases, TMP profiles were dependent on protein; in the absence of protein, the early sharp peak was replaced by a flatter profile with a later peak. Fractional effluent recovery (F; 0.77 vs. 0.82) and hepatic clearance (CL(H); 3.44 vs. 2.70 ml/min) for TMP were not influenced by albumin; with SMX, F increased (0.32 vs. 0.60) and CL(H) decreased (10.2 vs. 6.0 ml/min) with an increase in the perfusate protein concentration. Hepatic extraction of TMP was low (<0.30), whereas it was intermediate (<0.70) for SMX. In addition, distributional volumes and total water content of the liver were successfully determined.